1. Field of the Invention
The present invention relates to a synchronizing reproduction apparatus and a method of the same of image and sound data both coded in digital compression.
2. Description of the Related Art
In an image and sound synchronizing reproduction apparatus for decoding image and sound data coded in digital compression and reproducing both, all image and sound data can be reproduced continuously in the case where the data processing performance of reproducing apparatus is high enough. However, when the performance thereof is low, the image and sound data cannot be reproduced in real-time or in reproducing speeds as those originally have, since the times for data transfer and decoding process are required to some extent. That is, there arise problems that the image becomes a slow motion and the sound is reproduced intermittently.
Practically, since the congruity of the intermittent sound is higher than that of its image, the sound is processed in priority rather than the image in general so that the sound can be reproduced continuously. Thereafter, a process removed the sound reproducing process from the entire process is assigned to the image reproducing process.
At this time, since there arises problem that the content of image are shifted from that of sound unless the image is synchronized with the sound (or matched reproducing positions with each other), it is required to omit (or remove a frame) the decoding process of some frames in the image reproducing process.
As related to the synchronizing reproduction system of image and sound described above, there has been a system disclosed in a laid-open Japanese patent application No. Hei-7-50838. This system omits to read one compressed image data corresponding to the number of delay frames of the image and the other compressed image data which immediately follows the one compressed image data as far as a frame-in coded image without requiring a reference frame, at a time of making sure out of the synchronism in the case of arising it between the image and sound in a decoding device, as described above. That is, this means that the delay in image process is restored by removing frame.
In the coding systems for compressed image data there is one system for the frame-in coded image (hereinafter referred to as I-frame) without requiring a reference frame as described above, another system for a inter frame forward-directional predicting coded image (hereinafter referred to as P-frame) required a reference frame in the decoding and becoming a reference frame itself, and further another system for a inter frame bi-directional predicting coded image (hereinafter referred to as B-frame) required a reference frame in the decoding and not becoming a reference frame itself.
Assuming that the decoding for the I-frame and P-frame is omitted, the rest of those are decoded as a reference frame, but the succeeding P-frame and B-frame cannot be decoded correctly.
In the related art described above, when arising the delay of image process, since the decoding for the one compressed image data of the number of delay frames and the other compressed image data up to the I-frame immediately after the one, are omitted regardless of its coded system of the compressed image data, for example, when the data structure is of low frequency of appearing the I-frame, the number of frames to be practically removed becomes increased more than the number of delay frames, advancing a time of reproducing the image rather than a prescribed time. To this end, there may arise problem that the synchronizing control becomes rough. Therefore, in order that the synchronizing control is fine, the I-frame may be required to be previously and finely inserted into the compression-coded data when the data is generated.